Riddle me this:
A caster has a ring of invisibility.
He casts magic missile and becomes visible.
as part as his move action he then takes off and puts back his ring.
Becomes invisible again.
Screw greater invisibility.

For the sake of argument, if taking off and on a ring can be done as one move. (accounting for the little distance traveled by the ring)
The caster could at best do:
*Round one* casts magic missile and becomes visible. move action on/off ring
*Round two* reactivates ring,+cast non offensive spell.
Total time spent visible: All the time of the bad guys attacks.
Which makes this manuver pretty useless.

any way to make it work ?
What if: 2rings 1cup, no no, 2rings 1 unseen servant.

*Round one* casts magic missile and becomes visible. precast Unseen does the switch (his move) and i activate as... still does not work.